Arc welding is by far the most common welding process. The two main types of arc welding are submerged arc welding (SAW) and shielded metal arc welding (SMAW). In submerged arc welding, coalescence is produced by heating with an electric arc between a bare-metal electrode and the metal being worked. The welding is blanketed with a granular or fusible material or flux. The welding operation is started by striking an arc beneath the flux to produce heat to melt the surrounding flux so that it forms a subsurface conductive pool which is kept fluid by the continuous flow of current. The end of the electrode and the work piece directly below it become molten and molten filler metal is deposited from the electrode onto the work. The molten filler metal displaces the work and forms the weld. In shielded metal arc welding, shielding is by flux-coated electrodes or welding rods instead of a loose granular blanket of flux.
Fluxes are utilized in arc welding to control the arc stability, modify the weld metal composition, and provide protection from atmospheric contamination. Arc stability is controlled by modifying the composition of the flux. It is therefore desirable to have substances which function well as plasma charge carriers in the flux mixture. Fluxes also modify the weld metal composition by rendering impurities in the metal more easily fusible and providing substances which these impurities may combine with in preference to the metal to form slag. Practically all slag-forming compounds may be classed as either acidic or basic, according to which compounds they react with. The substances which are considered to be the most active "bases" are those which are compounds of the elements forming basic compounds in ordinary chemical reactions in water solutions, such as calcium, magnesium, and sodium. The most active "acid" impurities are compounds of silicon and phosphorous. Silicon dioxide (SiO.sub.2) is the only substance used as a strictly acid flux. Fluxes are prepared with a higher or lower percentage of acidic or basic compounds, depending on the type of metal to be welded and impurities in the metal. In some instances, other materials may be added to lower the slag melting point and to improve slag fluidity, and to serve as binders for the flux particles.
It follows that any improvement in welding fluxes or flux binders is of benefit to the many industries which utilize arc welding.
A problem encountered in the welding industry is the absorption of moisture by the flux covering on welding electrodes. Most welding electrode flux formulations consist of an oxide-based material (flux) and additives bonded together by sodium silicate (water glass). During welding, the heat evaporates and dissociates the water, evolving hydrogen gas, which dissolves into the metal. Under stress, the dissolved hydrogen may produce cracks with the potential for catastrophic failure.
In an effort to decrease the possibility of failure, the presently available welding electrodes are baked at 1100.degree. C. to decrease the water in the flux to less than 0.2%. These electrodes can then be used only for a limited time before the fluxes absorb moisture from the air and have to again be baked out.
A problem in addition to that of water absorption by these weld fluxes is their lack of a CO.sub.2 generating compound. CO.sub.2 aids in operability of the flux by increasing the stability of the arc and by excluding atmospheric contamination, particularly N.sub.2, from the metal. Baking at 1100.degree. C. decomposes sources of CO.sub.2, such as calcium carbonate, but does not allow diffusion of the calcium into the sodium silicate to form an intimate mixture which is non-hygroscopic.
Another problem with baking the fluxes at 1100.degree. C. to remove moisture is that metallic powders, which may be added to provide alloying of the weld metal, will oxidize during the baking operation. By lowering the necessary baking temperatures or by using less hygroscopic weld fluxes that do not need frequent baking, temperature sensitive alloy powders may be incorporated into the flux, thereby providing flexibility in the design of the fluxes.
Metal powders are added as required for alloying with the various types of metals or steels to be welded. Fluorides may be added to lower the viscosity of the flux at operating temperature thereby altering the fluidity of the molten flux on the steel. Flexibility in choosing the type of metal powders to be added to the flux rather than changing the composition of the steel rod decreases the cost of the welding electrodes.
It is therefore an object of the present invention to provide a welding flux composition which is not hygroscopic.
It is another object of the present invention to provide a welding flux which can be produced and processed at a temperature less than 1000.degree. C. so that compounds of low stability such as carbonate and alloying metal powders may be included.
It is yet a further object of the present invention to provide a flux which can be mixed with a number of different metal powders for alloying with different steels.
It is a still further object of the present invention to provide a binder for both shielded metal arc welding (SMAW) and submerged arc welding (SAW) fluxes.
It is another object of the present invention to provide a binder which yields a material with relatively high fired strength.